WiFi on steroids? First “WhiteFi” prototypes hit testing stage

Now that the FCC has opened empty TV channels to wireless networking, …

When the Federal Communications Commission (FCC) made the momentous decision late in 2008 to allow unlicensed broadcasting devices access to "white spaces" in the television spectrum, backers hailed the move as a major step forward for US wireless networking. "WiFi on steroids," was how one engineer put it during the debate.

But for white space devices to move from laboratory concept to store shelves, they would need more than steroids; they would need some sophisticated engineering. That's because the FCC imposed two critical conditions: whitespace devices must sense local transmissions from televisions and wireless microphones in order to avoid transmitting on those frequencies, and the devices must also access a geolocation database of known transmitters as a backup solution in case spectrum sensing failed.

Google, Microsoft, and others promptly got to work on the database, and spectrum sensing technology has already existed commercially for years. But how would a white space device—say, one located in the kitchen next to the family computer—actually communicate with the access point providing a connection to the Internet?

Such problems have already been solved many times over by wireless networking solutions as diverse as Bluetooth, 3G data transmission, and WiFi, so adapting one of the existing networking techniques to the new spectrum might seem like a no-brainer. But white space transmission features a host of challenges not found in conventional WiFi installations, challenges that meant existing WiFi protocols would not be optimal without some tweaking.

Microsoft Research's KNOWS team

Enter "WhiteFi," a proposal from Microsoft Research to create a WiFi-style system in which multiple clients can connect to a local access point operating in the UHF TV band. WhiteFi is the latest project to emerge from Microsoft Research's "Networking Over White Spaces" (KNOWS) project.

For its first trick, the research team handled mesh networking, in which each whitespace device connects to its neighbors, which connected their neighbors, to create a spontaneous local network. Recently, the team has turned its attention to replicating the traditional WiFi model (PDF) of a central access point with multiple client devices connected to it, but getting there required quite a bit of work.

The problems

The differences between WiFi and the white spaces go far beyond the difference in spectrum (WiFi operates most commonly at 2.4GHz and 5.0GHz, while white space devices can operate over 30 separate 6MHz TV channels in the UHF band).

For one thing, white space devices have to contend with far more "spatial variation" than does WiFi. As transmitters are moved around the neighborhood, city, or the country, the channels on which they can broadcast will change to avoid existing TV transmitters.

This creates more than regional variation. Imagine an access point that finds a clear space on channel 27 and begins accepting connections from client devices. But one of the client devices is one kilometer away in a location where a TV broadcast channel 27 can be faintly detected. The channel can't be used. The access point therefore needs to query all of the client devices when negotiating its data channels, making the system more complex than WiFi, which may need to worry about interference, but does not have to hop off any particular channel because of it.

A second (and related problem) is the variation of the data channels over time. Imagine an access point merrily transmitting data to five white space client devices in the neighborhood. Everything progresses swimmingly until someone at the church next door switches on a wireless microphone. The access point must immediately drop its signal on that channel and find a way to notify all of its clients about a move to some new (and clear) channel.

The prototype device

To find out just how many packets of data such wireless mics could handle before interference became audible, Microsoft researchers hauled one of their trial white space devices and a wireless mic down to an anechoic chamber. The results were not good; as the research paper puts it, "even a single packet transmission causes audible interference during wireless microphone transmissions."

In the real world, the problem might not be quite as bad, since transmitters and microphones will rarely sit within a few feet of one another, but it's still a serious issue.

Finally, white space devices face issues with spectrum fragmentation. While WiFi broadcasts on a single channel, there's no particular reason to do this when designing a white space device. In many locations, the available spectrum will feature several contiguous free channels, and if channels 25, 26, and 27 are all open, the device can get the most throughput by broadcasting on a wider spectrum or by channel bonding.

But this also poses problems; signals of varying widths take more time to detect, and the channel assignment problems noted above all get more difficult to deal with.

The solutions

The Microsoft Research team has addressed many of these issues with WhiteFi. First, the team crafted an efficient way to detect "variable-bandwidth signals," called SIFT. Then, it tackled spectrum assignment algorithms (finding and using the largest block of contiguous free channels isn't always the best technique, as some other white space devices might be transmitting on one or more of those channels, creating interference that could reduce speeds).

Handling disconnections, such as when a wireless mic suddenly pops on and forces a channel change, takes place using a special 5MHz backup channel. Whenever an access point or a client device detects an TV or wireless mic signal on a channel it is using, it stops transmission immediately and sends out a series of "chirps" on the backup channel. All access points and client devices check this channel every few seconds, and the chirps will help all the devices work out where to transmit next.

(Ah, but what happens when a wireless mic pops up on the "backup channel" itself? The researchers propose a secondary backup channel to deal with this situation.)

How does it all work? Pretty well, it seems. In the team's testing, the SIFT approach to channel scanning was 34 percent faster than the baseline approach. Channel disconnections were dealt with in under four seconds.

Such work is going on among various white space developers (Motorola and Philips are working on devices, for example), but it's also taking place at the IEEE, where engineers on the 802.22 working group are developing techniques for Wireless Regional Area Networks over the TV white spaces.

We're still some ways from seeing devices on store shelves, but with a projected 1km transmission distance and the promise of broader transmission channels, white space devices are shaping up into some promising technology. Once seen largely as a way to offer fixed wireless connections to rural homes, white space devices will soon be able to create mesh networks and WiFi-like connections—that early promise of "WiFi on steroids" might turn out to be surprisingly accurate, after all.

39 Reader Comments

Following wireless technology is like trying to hold on to the side of a train flying 200 miles an hour down a twisting track. I wonder what new benefits we will see come out of this technology besides simplying gaining access to larger networks. I love the idea of mesh networks, perhaps now wireless technology will be as reliable as wired technology.

Nice to see development of this kind incoming! WRAN on UHF would kick asses, especially if they work on a mesh-style IPv6 network. It would redefine completely the net as we know it. People could expose servers on to their locals without paying bandwidth fees. Accessing the net could be done by routing it's traffic through a particular wireless node that the ISP of your choice would have set up. Wonder what kind of bandwidth UHF can hold per channel.

Originally posted by gamefreak:WiFi on steroids? Range sure...But correct me if wrong but at 6 Mhz won't there be an ABSOLUTE bandwidth limit at about 6 Megabits? (As in 1 bit per cycle.)

It depends upon what sort of keying you are doing. If you were transmitting data as 1s and 0s at 6 MHz you'd be stuck, but if you are using PSK (http://en.wikipedia.org/wiki/Phase-shift_keying) you can stuff more bits than you otherwise would have been able.

Additionally, using the channel-bonding described in the article, it sounds like it would be possible to add another multiplier to the available bandwidth.

Of course, I'm not an RF engineer so everything I said could be entirely wrong.

Working in the professional audio business, using Wireless equipment has always been a challenge, but instead of having to dodge a few TV stations, I have to dodge every idiot that sets one of these up. It's 900 MHz all over again...without the freaking baby monitors.

And there was no technological breakthrough here. The professional wireless audio manufacturers have been providing mechanisms for years that identify available whitespace.

And let's be honest, how many Wireless Networks do we need? We have WiFi at 2.4 and 5, Cellular at various carrier frequencies, and WiMax (2-11).

Speed? For local networks, I get the need, but when the backhaul is usually less than peak for B, much less G or N, it is simply overkill.

Range? With the right antenna configuration, I have been able to push B out to a quarter mile, and much further with directional antennas.

This is just another money grab by groups like MS looking to bypass the cellular carriers and avoiding the IP, and technical headaches of WiMax.

After Kevin Martin forced through white space devices over the advice of many reputable RF engineers, now they're going to get to deal with the reality of the situation, which is that it will not work.

They'll try it, don't get me wrong, but it will mangle TV reception and prove itself to be utterly useless or totally destructive in practice. I expect more of the latter than the former.

The biggest problem they're going to run into is that in large parts of the Los Angeles area, there are no white spaces. Period. I suspect this will turn out to be true in a lot of major cities, if not now, then soon enough.

In rural areas where there are "empty" channels, the new close-range signals will raise the noise floor, destroying some or all of what little TV reception viewers in those distant areas had, assuming anyone bothers implementing them in the first place.

White space devices: A problem, disguised as a solution, looking to fix a problem that it can't solve.

Well, some folks on Ars think this is a bad idea, and they clearly know more about this than anyone doing R&D on it at a paid facility. So, this research into this technology clearly needs to stop, and we should all go back to doing something more productive, like digging ditches with our hands.

I have said this before on this subject and I'll say it again, do research on the damn thing before you write an article that is not accurate, and before you cheer on something that is full of problems.

They are back to champion wireless detection at the same time talking about transmission ranges of 1km. How about when that wireless mic is turned on and the nearest transmitter is a 1/4km away. What do you think the odds are that the transmitter will detect that mic? It won't because it's detection will be limited to the sensitivity of its transmit and recieve antenna, which will be located in a structure such as a house and at 150 meters the weak signal of the mic would be undetectable above the ambient noise floor. So it'll stomp all over that mic signal. I've yet to see info on how to register a mic in the database, I've yet to see any of the beacons, so how are they suppose to defend against interference?

Top that off with IM3 interference which will be huge if they start bonding channels, hell I never thought they'd try that, but apparently they are. Anyone in that 1km area that is in a borderline DTV reception area will not be getting a picture the first time one of these things bonds a channel. All I can say is it'll be a huge huge mess for sports events and concerts and major cities.

But hell, they didn't listen to any of our complaints during the testing even when the tests showed we were right, so I hope they are ready for a nice backlash from the public when this stuff goes live.

@tripinvaCuz you know, all the engineers on the other side of the argument were talentless hacks.

They've got a working protocol. Whatever ends up moving into the market will be IEEE approved and FCC licensed, which is more than can be said for the wireless microphones that they are trying so hard to avoid interfering with.

The real question here? How does "Networking Over White Spaces" get KNOWS as an acronym? What is the "K"?!?

If this tech doesn't work up to its billing, there'll be a political and economic decision to make. Until then, keep the research going. Although I don't have that much sympathy for wireless microphones anyway; use wires or get your own spectrum license, don't complain about someone else mooching the same bandwidth you are.

On the other hand, what I wonder about with 'white-fi' is how useful it will be if everyone in a 1km circle is sharing a handful of 6Mb bands. That doesn't sound viable to me - the B/G band is useless in my building, and that's just dealing with people in the nearest 100 metres.

Originally posted by bedward:If this tech doesn't work up to its billing, there'll be a political and economic decision to make. Until then, keep the research going. Although I don't have that much sympathy for wireless microphones anyway; use wires or get your own spectrum license, don't complain about someone else mooching the same bandwidth you are.

On the other hand, what I wonder about with 'white-fi' is how useful it will be if everyone in a 1km circle is sharing a handful of 6Mb bands. That doesn't sound viable to me - the B/G band is useless in my building, and that's just dealing with people in the nearest 100 metres.

As a tv broadcaster I have a spectrum license for both my DTV transmitter and for my wireless mics. Those mics are used in situations where you simply can't be wired with any sort of ease if at all, and since they are used in live shots, they are not in a fixed location. We always run cables for anything we can, but you simply can't do it for everything. Concerts and Sports event are two other major users of wireless mics and wireless intercom for stage personal. The intercom stuff is very critical in that if it goes out, there can be safety issues. Its not practical for a stage hand to drag a wire with them. As to digital, its called delay and fidelity, all forms of digital transmitters have unacceptable amounts of latency and nothing has come close to fixing it, thus it is all still analog.

Don't put words in my mouth (on my keyboard?). I never said that. In fact, I don't think I said anything at all about wireless microphones either. Since I don't know anything about that subject, I prefer not to comment on it. Meanwhile, I've done extensive TV engineering work including answering phone calls and resolving DTV reception complaints after June 12.

What I will say is that the FCC's own engineers were forbidden from attending the meeting where Kevin Martin approved white space devices. I have heard plenty about the testing and read the OET's report, and the fact is that the stuff does not work as promised. In fact, most of the gear failed the testing that was required before the decision was to be made.

I also did not like the policy the FCC has made with regard to what frequencies are "open." Basically, even if a white space device detects the presence of an OTA TV signal, it's still allowed to transmit on that frequency so long as you're outside a certain line that the FCC specifies which has no basis in reality. So for example, where I live, only my PBS, ABC, and CW station are protected. All the other networks, which are 100% on my receivers, can be demolished by white space devices and still be legal according to the FCC's rules, simply because I'm outside some theoretical line.

Hopefully white space devices will join BPL as a technology that failed.

The typical reception range for the wireless gear we use is at best 100-150 feet in most areas we use it. It typical use we are usually only covering distances of 35-40 feet or less. Transmitter power is only 50 milliwatts. The most powerful mic setups I'm aware of max at 250 milliwatts and those are typically only found it setups like a NFL game where its needed for the extreme range.

Compare that to the whitespace devices which were listed as between 1-4 watts power, and I'm not certain what the ERP output of those devices are, it will depend on the type of antenna they use, assume it'll be a dipole of some sort. It'd be like you standing in your yard talking with a megaphone on max volume and stopping when your nieghbor across the street starts whispering in his living room. You'll never know when he whispers because you have no way to detect it as its to faint to be dectected above the noise threshhold.

Originally posted by bedward:That's a possibility I never considered - I stand edumicated.

So you don't run into trouble with other people's analog wireless mics? I guess the range must be just too short for that to be an issue.

Wireless mics generally put out in the region of 30mw, and have limited range. There are some situations where you use much higher power transmitters, in the region of 1w, however these are generally at large outdoor events and the spectrum is specially licensed for the event.

I hope to god OFCOM never try and allow these devices in the UK, there's been enough trouble with them clearing the 800MHz band to sell it to the highest bidder probably mobile telecoms.

Echoing other's there are digital wireless mic systems on the market however they have a latency in excess of 4ms which is completely intolerable for live sound re-enforcement. Broadcast could probably cope by spending money in order to delay the video by the same amount, but why bother when analogue mics have delay measure in the microseconds and are a far better solution.

On a completely non-technical, superficial level ... White-Fi is a dumb name. While I will admit technical folks tend to come up with better tech names than marketing "guru's" ... white-fi? really? Hmmm...

Originally posted by bedward:If this tech doesn't work up to its billing, there'll be a political and economic decision to make. Until then, keep the research going.

This.

I have no idea where the "it'll never work" brigade are heading - it's not finished yet ! To derail it at this stage, would be absolute loonacy - if by some miracle it is made to work, then we'd all miss out.If on the other hand, they can't overcome the problems - then ditch it.

Originally posted by bedward:If this tech doesn't work up to its billing, there'll be a political and economic decision to make. Until then, keep the research going.

This.

I have no idea where the "it'll never work" brigade are heading - it's not finished yet ! To derail it at this stage, would be absolute loonacy - if by some miracle it is made to work, then we'd all miss out.If on the other hand, they can't overcome the problems - then ditch it.

We understand antenna sensitivity pretty well, and it's pretty straightforward to see that transmitter A can be close enough to transmitter B to receive interference, but not close enough for transmitter B to detect transmitter A. It's even easier when transmitter A uses 1/10 the power of transmitter B.

Transmitter B is a 'white-Fi' device. transmitter A is one of windnwar's wireless mics.

Please, if you know of a solution to this problem, let us know. Amateur radio operators, TV and commercial radio operators, and the US military would love to have this one solved. They'd pay you phenomenal amounts of money if you could take care of this for them.

Look, I'm an amateur radio operator but I'm no expert at RF. I also don't watch TV, so WSD interference with TV and wireless mics isn't going to affect me directly. I'm also not opposed to more efficient spectrum usage. Finding ways to use that scarce resource more efficiently is cool, and I really like technological advancement.

But I'm also suspicious: there are significant technical issues that have simply never been addressed in a serious way by those backing WSDs, and ignoring them doesn't make them not real.

I was considering whether should even bother posting on this topic again or not at this point...

However I figured I should clarify some things.

One, windnwar I really didn't have much problem with the article. It wasn't trying to address much other than just to say this is what is going on with the current research being done.

Now some of the comments as usual might display a bit of lack of knowledge on it, but that is to be expected.

quote:

Wireless mics generally put out in the region of 30mw, and have limited range. There are some situations where you use much higher power transmitters, in the region of 1w, however these are generally at large outdoor events and the spectrum is specially licensed for the event.

You and windnwar are both correct in as far as the majority of wireless microphones are in th 30-50mW range.

However you are incorrect on the maximum allowable power. 1W would be correct for a low power auxilary broadcast, IF, it was not in the TV Band frequencies. However as defined by 47 CFR 74.861 devices in TV band frequencies (In the US, note that I don't know the regulations for the EU form OFCOM), which is where wireless microphones live and white space devices are aimed for, are limited to 250mW. However obviously the white space devices are most likely going to be authorized with much more power and fall under different regulations.

By the way, small side note... The FCC Part 74 defines low power auxiliary broadcast devices (Which wireless mics fall under) as being intended to broadcast at a range of about 100 meters. 1/10 of the range being discussed here, and that is when talking about a full power (250mW) transmitter as I mentioned before.

quote:

Except these devices do that themselves already.

There are still many concerns not addressed by the testing that both windnwar and myself have brought up in the past. The basic physics of a device broadcasting at 1/10th of the power of WSD being detected by the WSD works very much against the detection. Add on to this that other concerns such as IM from broadcast have not been addressed at all, and is a major factor here, it is wrong to think that even the basic concepts have been hammered out in full.

quote:

So beyond wifi with to short a range, how many of those can I as consumer setup?

As mentioned WiFi doesn't necessarily have short range, but on top of that there is at least one more that can be, and that is a network in the 900MHz unlicensed frequencies. The catch is that it is not used much because... surprise... those frequencies are very crowded as is and interference becomes a major issue.

quote:

I'm glad you could, are you trying to claim that this would be possible for everyone everywhere?

Going off topic here...

Yes. It is much like setting up an satellite connection, which I was doing when I was a kid(Talking 10-12 years old here). It is not extremely difficult, and yes there are companies that will set it up for you as well in many areas.

Like satellite there ar geographical limitations in as far as setting it up, but thus far I have seen more success stories than failure stories if it is planned out.

quote:

Well, some folks on Ars think this is a bad idea, and they clearly know more about this than anyone doing R&D on it at a paid facility. So, this research into this technology clearly needs to stop, and we should all go back to doing something more productive, like digging ditches with our hands.

You might be surprised what professionals dealing with wireless microphones learn. I know quite a few people I would trust their combination of engineering knowledge and hands on experience over most people's. And yes many professionals dealing with this hands on are in fact RF engineers, and hold a degree in engineering, just like those folks in the lab working on the research. This includes a couple of people that I know have at least read Ars in the past, even if they have not commented publicly.

So yes, thinking is a good thing, and realizing that just because someone posts on Ars doesn't mean they automatically must know nothing about the topic.

(For the record, I do not hold an engineering degree. I do however consult often with people that do

bedward-

There is more political mistakes than anything in the entire history of wireless mics. As windnwar pointed out many users of wireless microphones are in fact licensed users under Part 74 as a low power auxiliary transmitter. When wireless microphones were put to use in other sectors that section of the licensing requirements was never updated. In order to obtain a license you technically should be a licensed broadcaster, though many people have slipped in under a 'distribution' loophole in there somewhere(To lazy at the moment to find the wording). But the fact of the matter is that it was never updated for live uses that were not broadcasters and thus unlicensed use became common. The FCC then turned a blind eye to this usage for multiple reasons. Namely it was easier to do that than to update the regulations, and because wireless microphones are such low power they rarely, if ever, cause a problem because by the time they do they are useless themselves. I posted in depth about this in the past, do a search for my name and white space and you will probably find more information than you ever want to know.

Wireless microphones have to be carefully coordinated when dealing with multiple microphones for problems, not only the obvious stepping on used frequencies, but in particular inter-modulation, of which IM3 is the largest problem maker in there, however other forms of inter-modulation exist as well that mean coordinating 20-40 channels or more becomes a chore(To put it mildly) in the best of conditions. Add in white space devices causing their own IM and jumping around while doing so, meaning that there will be no good way to predict this, means that things are going to get MUCH more difficult no matter how yo look at it. Just avoiding frequencies in active use is only part of the problem. Not causing interference on other frequencies from inter-modulation is a much more difficult second part of the problem that has never been addressed.

That is part of why wireless microphone users in particular are more than slightly troubled by this still.

Originally posted by Nom:I have no idea where the "it'll never work" brigade are heading - it's not finished yet ! To derail it at this stage, would be absolute loonacy - if by some miracle it is made to work, then we'd all miss out.If on the other hand, they can't overcome the problems - then ditch it.

The problem is, as I alluded to in my post, many things don't seem to be considered at all in this 'research', most notably IM interference on transmission. You will note that this was not addressed in the FCC field tests by the OET either, only reception and detection. Transmission was extremely minimally tested and what was shown was that interference was a major concern on overlapping transmissions, for a LARGE distance. Nothing else was tested, and even that wasn't really supposed to be part of the official tests.

So there is definitely reason for concern even at the 'research' stage when not all factors are actually being looked at from what I can see.

Everything progresses swimmingly until someone at the church next door switches on a wireless microphone. The access point must immediately drop its signal on that channel and find a way to notify all of its clients about a move to some new (and clear) channel.

And the wireless mike doesn't just switch to a clear channel instead of the access point because???

Everything progresses swimmingly until someone at the church next door switches on a wireless microphone. The access point must immediately drop its signal on that channel and find a way to notify all of its clients about a move to some new (and clear) channel.

And the wireless mike doesn't just switch to a clear channel instead of the access point because???

Because the wireless mic has no way to detect what channels are in use. It will simply get its signal stomped on by the WSD. And in the case of licensed mics like mine, being I have a license to be there, and the WSD doesn't, it is the one that has to move. The only thing I have to move for are other licensed primary users of that spectrum. Now in practice if I detect interference I will move my channel to an open place, however since the WSD's will move to whatever they find open, they are a moving target, and might step on me again on their next move. Or if they bond a few channels together, the IM3 might squash a whole range of channels I'd otherwise be able to use.

By the way Seablade, I didn't have a problem with most of the article, but I do have issues with any time detection is brought up as something that works and has been around for awhile. Throwing that in there, basically gives the typical reader the idea that this is basically all sorted out, we just have to figure out which method we want to use for the network topology now.

I can only imagine the interference these things will cause in the wild with channel bonding. Its going to be a mess to see.

Everything progresses swimmingly until someone at the church next door switches on a wireless microphone. The access point must immediately drop its signal on that channel and find a way to notify all of its clients about a move to some new (and clear) channel.

And the wireless mike doesn't just switch to a clear channel instead of the access point because???

Because the wireless mic has no way to detect what channels are in use. It will simply get its signal stomped on by the WSD. And in the case of licensed mics like mine, being I have a license to be there, and the WSD doesn't, it is the one that has to move. The only thing I have to move for are other licensed primary users of that spectrum. Now in practice if I detect interference I will move my channel to an open place, however since the WSD's will move to whatever they find open, they are a moving target, and might step on me again on their next move. Or if they bond a few channels together, the IM3 might squash a whole range of channels I'd otherwise be able to use.

To add on to this before it gets brought up, a wireless mic adopting the same strategy is not an option because a wireless mic demands constant transmission, otherwise you get dropouts which sound like really nasty pops throughout audio, if you are lucky, but in this case you would probably get bursts of static as well.

People doing professional wireless microphone stuff just need to buy a frigging $10 WhiteFi detector/compatibility box! How hard can it be. If you are a sound professional, get one of these boxes and join in the global interference-free WhiteFi management!

WhiteFi is designed to work even for the morons using UHF microphones without one of these boxes in their profimity. But if you care about your wireless microphone usage, then just get a frigging $10 box and turn it on BEFORE you want to use a mike!

This $10 box will simply warn all WhiteFi users in the area that they simply need to switch over to another available channel for an uninterrupted WhiteFi experience. Otherwise, if you are a sound engineer moron wannabe who doesn't want to purchase a $10 add-on WhiteFi channel presence emitter box, when you turn on your microphone, WhiteFi devices on that channel will instantly switch off that channel and it'll take less than 4 seconds for all of them to switch over to another channel.

The truth about this is that NAB and Microphone lobby are in bed together and that they will fight with Telecom and ISPs for as long as they can to stop WhiteFi from happening. The reason being that when WhiteFi is activated and in use everywhere following will happen:

- Wireless voice services in new phones, no more AT&T/Verizon/T-Mobile/Sprint required for mobile telephony. Wireless voice services will be over-IP and free. A multi-trillion dollar industry killed right there.

Originally posted by Charbax:This $10 box will simply warn all WhiteFi users in the area that they simply need to switch over to another available channel for an uninterrupted WhiteFi experience. Otherwise, if you are a sound engineer moron wannabe who doesn't want to purchase a $10 add-on WhiteFi channel presence emitter box, when you turn on your microphone, WhiteFi devices on that channel will instantly switch off that channel and it'll take less than 4 seconds for all of them to switch over to another channel.

I had something typed out, but then read hpsgrad's post and realized maybe I am misreading your post and you are being sarcastic. If you aren't, feel free to post up again and I will be happy to explain the multiple reasons why this isn't an answer.

Then get white-space devices licensed for the spectrum and get OTA TV broadcasters licenses revoked. If you can't get that far, then I think it safe to say that not enough people agree with you to accept the interference that these devices will almost certainly cause (to each other as well as to licensed users).

Remember, white-space devices have shown no ability to revolutionize internet access. That's all hype from people who want to sell them, so far. Those people appear to have simply ignored real technical problems with their plans (saturation of white spaces could happen a lot faster than anyone wants to think about, interference could easily be bad enough that licensed users of that spectrum complain to the FCC, etc., etc.) and point at their receiver/antenna sensitivity to OTA TV signals (as tested by the FCC's OET) and say 'look, we've solved the problem!'

I'd love for WSD's to work, it'd be great for all sorts of people. I'm skeptical, and so far those backing the devices have had nothing more than cheerleading (and, in the case of Tremelune, arrogance) to answer that skepticism. This is not encouraging.

Originally posted by Brothernod:I have a feeling this conversation is dead (I'm late to the party) but I have a stupid question I'd love an answer too after reading this whole thread.

White Space Internet is possible because the spectrum that was used by broadcast TV has been vacated thanks to DTV. Yes?

No. The spectrum vacated by TV broadcasters has been auctioned off to other licensees. The big cellular carriers picked up most of it, IIRC.

quote:

Brothernod:Previously wireless mic's existed during the time where tv was broadcast over the analog spectrums.

Why can't the internet just step in where tv left off?

It's because there are significant differences in the way that WSDs and OTA TV broadcasts work. OTA broadcasters would be licensed to use one channel (or two, or whatever). The FCC allocates channels to coordinate TV broadcasts across the country, and to minimize interference created by those broadcasters. Because of the way RF works, minimizing interference requires leaving open channels between those in use. So, you'll never see TV channels 6, 7, and 8 all in use at the same time. At most, you'll see 6, 8, with 7 left as 'white space' to prevent interference.

This is the 'white space' that WSDs are using. This is also the space where certain wireless microphones are active. Some of those wireless microphones are being used by licensed broadcasters (windnwar is one, for example), and are 'legal' to use this spectrum. They don't interfere with OTA TV broadcasts (or other wireless mics) because:1. they are very low power2. the users tend to be knowledgeable professionals who check the channels in use to minimize the chances of interference

WSD's are different because:1. they're much higher-power than wireless mics2. they're going to be deployed much, much more widely than wireless microphone systems3. those deploying them will mostly have no clue that their WSD could interfere with anything, and wouldn't have the equipment to check for interference even if they did.

The manufacturers of WSDs claim that their sensor technology, combined with a database of licensed users of TV channels (including those licensed microphone users) will mean that interference by a WSD won't happen. Unfortunately, nobody's tested that claim in anything like a real-world manner, and the tests that have been conducted don't address significant issues regarding frequency saturation, intermod interference, and the problems of detecting a signal an order of magnitude weaker than the signal you're broadcasting.

I hope this summary is accurate and helpful. If it's not, I expect I'll be corrected shortly.